Post on 27-Jan-2016
description
Ivo van Vulpen
Looking beyond the horizon using top quark physics at the LHC
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 2
2) Roadmap to discovery:
SM: Top quark physics at √s =14 TeV
Beyond: Anomalies in top quark events
Layout talk
1) Motivation: the SM and beyond
3) Workplan
VIDI proposal
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 3
The Standard Model & the Higgs boson
• The Standard Model: - Combines the EM, weak and strong force - Describes all measurements down to distances of 10-19 m
• Electro-Weak Symmetry Breaking: (Higgs mechanism)- Weak gauge bosons and particles have mass- Regulate WW/ZZ scattering
4222V
“We know everything about the
Higgs boson except its mass”
Λ (GeV)
Hig
gs m
ass (
GeV
)
Triviality
Unitarity
Limits on mh from theory
Limits on mh from exper.
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 4
“All measurements in HEP can be explained using the SM”
Many open questions in SM.… but also things we do not understand: Gravity, Cold Dark Matter, Why 3 families, Why mt » me » mν
Higgs: 1) Higgs has not been discovered 2) Even if we do: hierarchy problem, or “Why is MEW « MPL ?”
“The Higgs boson will be discovered at the LHC at ~ 150 GeV”
NO !
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 5
The hierarchy problem
Hierarchy problem:
‘Conspiracy’ to get mh ~ MEW (« MPL)
Biggest troublemaker is the top quark!
4532-
129
91 boson Higgs
9.2 172.7 179 quark top
?
predicted observedW W
b
t
...δmm toph,hbare
22
2toph, 8
3m t
h h
t
λt λt
Radiative corrections from top quark
Λ2
150 = 1354294336587235150
–1354294336587235000
mh =
• Failure of radiative corr. in Higgs sector:
• Success of radiative corr. in the SM:
Solutions to the hierarchy problem
Little Higgs
Higgsless
mSUGRA
GMSB
AMSB
Extra Dimensions
?
Standard Model
SUSY
(MPL is a few TeV)
(boson loops cancel fermion loops)
(several new particles)
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 7
Main idea / approach
• Idea 1: Do not concentrate on a specific model (model 1,2, …) Look for fingerprint of new physics in specific topology
SM
Data
model 1
model 2
model 3
model 4
model 5
model 6
Anomalies
SM
model 4
tt
• Take a topology that is:
- a well calculable SM candle - sensitive to several hypotheses simultaneously
Most models predict signature visible in top quark pair production
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 8
The ATLAS detector at the LHC
T - 500 days …
Luminosity per year: 2007: 100 pb-1
Nominal: 10 fb-1
The LHC collider:
The ATLAS detector:
First year: Enormous reach for new physics. Need to understand detector and
SM at √s =14 TeV.
Process #events #events sec-1 10 fb-1
3 3TeV)(m
4 TeV) 1g~(m
5GeV) 130h(m
8
8-
8
126
10 0.0001 BH
10 0.001 g~g~10 0.02 h
10 1 tt
10 1.5 μ/μeeZ
10 15 eνW
10 10 bb
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 9
2) Measure top properties:
Charge, couplings, mass, cross section, ….
3) Use tt events as a calibration tool:
Complex topology with multiple constraints
Top physics at the LHC
1) Top production at the LHC:
85 % TEVATRONLHC )tσ(t 100 )tσ(t
7.5 million events/year
NLO Monte Carlo
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 10
Top physics at the LHC
Calibrate missing ET
Obtain enriched b-jet sample
Leptons & Trigger
Calibrate light jet energy scale
2) A candle for complex topologies:
4/9
“Top quark pair production has it all”:
≥ 4 jets, b-jets, neutrino, lepton several mass constraints for calibration
Note the 4 candles:
- 2 W-bosons Mw = 80.4 GeV- 2 top quarks & Mt = Mt-bar
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 11
LHC day 1: See the top
• Standard-analysis: 2 b-jets S/B ~ 80
• Commissioning-analysis: no b-tag (robust cuts)
Mjjj (GeV)
L=100 pb-1
Even
ts /
4.1
5 G
eV Hadronic 3-jet mass
ATLAS
mtop
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 12
LHC day 2: Resonances ?
• Structure in Mtt
Interference from MSSM HiggsesH,A tt (6-7% effect)
Cro
ss s
ecti
on
(a.u
.)
Mtt (GeV)
• Resonances in Mtt
Resonance of 1600 GeV
# e
ven
ts
Δσ/σ ~ 6 %
ttXpp
Z’, ZH, G(1), SUSY, ?
Mtt (GeV)
400 GeV
500 GeV
600 GeV
Gaemers, Hoogeveen (1984)
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 13
LHC day 2: First to discover SUSY
Topology: ≥4 jets missing ET (large) leptons/photons
SUSY events are in top sample!
jet
01 0
1jet/lepton
jet/lepton
jet
jet
In R-parity conserving models the LSP is stable and escapes detection (mSUGRA)
• Sensitive to hard scale:
i
N
1iTTeff )(PE M
jets
After 1 year reach ~ 2 TeV for MSUSY
# e
ven
ts/4
00
GeV
Meff (GeV)
SUSY Discovery
ATLAS 10 fb-1 (1 year)
tt production dominant backgroundremember: we understand this
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 14
Plan of research
Develop constrained
fittingpackage
Resonances in
tt
tt
M d
σ dExtra leptons in tt-like events … SUSY
• Improve lepton identif. and trigger in multi-jet events
• Calibrate missing ET
• Reconstruct total tt-system. Measure differential cross section.
• Calibrate Jet energy scale
• Select clean b-jet sample
Commissioning analysis: 4 jets+lepton +missing ET
Investigate leptonic side
InvestigateHadronic-side
1) Prepare for first data:
- Calibration strategy & trigger - Constrained fitting - Weltmeister!
2) SM Top physics:
- Cross section (leptons) - Jet energy scale
3) Beyond the SM:
- Structure in Mtt
- SUSY with leptons - ?
2005
2006
2007
2009
2008
2011
2010
Plan of work
Rediscover the topconfidence!
Possibility to divert interest quickly if anomaly appears in unexpected topology
BONUS
Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 16
Summary
Base scenario:
Top physics: Important scientific program!
Hint of new physics elsewhere: extra information from top sector
New physics strong in top sector discovery!
Great scenario:
Perfect scenario: